freopen用法

#include <bits/stdc++.h>
using namespace std;
int main()
{
    freopen("1.in","r",stdin);
    freopen("1.out","w",stdout);
    int n;
    scanf("%d",&n);
    printf("%d\n",n);
    fclose(stdin);//关闭重定向输入 
    fclose(stdout);//关闭重定向输出 
    return 0;
}